1. Field of the Invention
This invention relates to a turbine control device which compensates for non-linearity of the degree-of-opening/flow-rate characteristic of a turbine regulating valve.
2. Description of the Prior Art
In general, the output of a steam turbine is regulated by using a regulating valve to alter the flow rate of the steam flowing into the turbine. However, the degree-of-opening/flow-rate characteristic of the regulating valve is normally non-linear, with a differential coefficient that is a maximum at the start of opening and which tends to drop as the valve gets closer to being fully open. The turbine control device is, therefore, usually provided with a function generator to compensate for this non-linearity. This will be described with reference to FIG. 1.
Inflow of steam generated in a boiler 10 into a turbine 12 is regulated by a regulating valve 14. The steam that flows into the turbine 12 rotates the turbine 12, driving a generator 16 and generating electric power.
The actual speed of the turbine 12 is detected by a speed detector 18. A deviation calculator 20 makes a comparative calculation with a speed value set by a speed/load setter 22. The deviation between this set speed and the actual speed is converted into a flow rate instruction by a speed controller 24 and sent to a function generator 26. Based on a preset function form, the function generator 26 converts the flow rate instruction into a valve degree-of-opening instruction, which is then sent to a servo controller 28. The servo controller 28 controls the degree of opening of the regulating valve 14 in accordance with this valve degree-of-opening instruction. Thus, the turbine 12 is controlled to a prescribed speed based on the degree of opening of the regulating valve 14.
In such a turbine control device, the function generated by the function generator 26 to compensate for the non-linearity of the degree-of-opening/flow-rate of the valve was conventionally set only with reference to the design data of the regulating valve. As a result, in many cases it would either overcompensate or undercompensate and it was difficult to obtain proper linearity. Furthermore, as this function generator was realized by a mechanical cam or electrical polygonal line function generator, resetting to adjust to operational data was difficult, and could only be carried out after shutting down the turbine. This wastes a lot of time and reduces the life of the turbine rotor.